In a wild final-round shootout on the US Labour Day, Kirk fired a flawless five-under-par 66 at the TPC Boston to win the second of four lucrative FedExCup playoff events on the US circuit.
The 29-year-old birdied the 13th and 16th to pull two strokes clear and narrowly missed another birdie attempt, from nine feet at the last, to post a 15-under total of 269.
Kirk not only claimed his second US PGA Tour title of the season but he took over at the top of the FedExCup standings and advanced his claims for a late Ryder Cup call-up by US captain Tom Watson on Tuesday.
"Just unbelievable," Kirk, who outshot Rory McIlroy by four shots in the final round after being paired with the world number one, told NBC Sports. "My biggest win ever.
"I was just trying to go play like I did yesterday," said Kirk, referring to his third-round 64. "Obviously I didn't shoot quite as low as yesterday but I really felt good with the putter today."
Billy Horschel bogeyed the final hole, after hitting his second shot into a hazard, to card a 69 and finish joint second at 13 under with fellow American Russell Henley (70) and Australian Geoff Ogilvy (65).
McIlroy, who began the final round just two strokes off the pace in pursuit of his fourth PGA Tour victory in five starts, had to settle for a share of fifth place at 11 under after closing with a 70 that included five birdies and four bogeys.
Henley had been a stroke in front of the chasing pack overnight and was briefly caught at the top by Horschel before he edged ahead by sinking a seven-footer to birdie the par-five second hole.
Horschel again pulled level, with a birdie at the par-five seventh, before being handed the outright lead when Henley bogeyed the par-three eighth after his tee shot ended up in a greenside bunker.
Kirk joined Horschel at 13 under when he picked up his third shot of the day at the ninth, sinking an 11-footer, before Ogilvy made it a three-way tie at the top when he birdied the 13th.
Brilliant birdie putts from 23 feet at the 13th and from 13 feet at the 16th put Kirk two ahead and, though Horschel briefly cut the deficit to one with a birdie of his own at the 15th, Kirk maintained control with a par-par finish.
Horschel had been bogey-free in the final round until he dumped his second shot at the par-five last, a six-iron from 212 yards, into the hazard guarding the front of the green.
"The worst swing I've made all week," said the 27-year-old American, who was seeking a second career victory on the PGA Tour.
"My ball was a little bit below my feet, uphill lie, and I just wanted to make sure I stayed in the golf shot. I knew anything on the green or in the right bunker was good, I was trying to make sure I hit a good golf shot.
"It's unfortunate. I played really good today, not to make a bogey until 18. A lot of good stuff happened today ... it just wasn't my day, I guess, hitting that bad of a shot."
The triumphant Kirk now faces a waiting game until U.S. captain Watson announces his three wildcard picks on Tuesday to complete the 12-man team to take on holders Europe at the Sept. 26-28 Ryder Cup in Gleneagles, Scotland.
"I definitely have put myself in contention for one (of the picks)," said Kirk, who would be a Cup rookie if selected. "If I get picked, great. If not, then I am still very happy with my win today."
The top 70 players on the FedExCup points list after the Deutsche Bank Championship advance to next week's BMW Championship in Englewood, Colorado where the leading 30 will qualify for the Sep. 11-14 Tour Championship finale in Atlanta.
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